SpaceX is a private company, once it has been paid money that money is SpaceX's and is not taxpayer money any more. It's been spent. If the government hired a contractor to build a road, paid them to do so, and then the contractor took the money they'd been paid and invested it in some other company that the contractor owned, is that "corruption?"
Insert standard disclaimer here; Elon Musk is a terrible person and he's made a lot of terrible decisions, etc. and so forth. It's not going to stop me from being called a bootlicker, not sure why I bother inserting it.